[Oncogenic osteomalacic myopathy; a case report].

Abstract

A 54-year-old man with oncogenic osteomalacic myopathy was reported. He presented with gradual onset of muscle weakness and painful cramp of the bilateral quadriceps femoris muscles, followed by low inorganic phosphorus, elevated alkaline phosphatase in the serum and hyperphosphaturia. The electromyogram (EMG) revealed myogenic change localized in the quadriceps muscle and nerve conduction study was normal. Muscle biopsy of right vastus lateralis muscle demonstrated non-specific myopathic change with minimal neuropathic change: moderate variation in size, many centrally placed nuclei, a few small angulated fibers and pyknotic nuclear clump. The ratio of Type IIA fibers decreased to 5.5%. Serum 25-hydroxyvitamin D and parathormone were normal, whereas 1, 25-dihydroxyvitamin D was above lower normal limit. High dose of 1,25-dihydroxyvitamin D and phosphorus were administered with partial response. CT scan demonstrated tumor in the left 10th rib proximal to the vertebra, invading into the mediastinum. Partial resection of the tumor was performed in order to preserve the rib. Histologically, the tumor was characterized by high vascularity with cystic formation, many giant cells and tumor cells with oval-shaped nuclei. Histopathological diagnosis was primitive mesenchymal tumor (mixed connective tissue variant). Immediately after resecting the tumor, the patient's muscle weakness and painful cramp was prominently relieved and serum inorganic phosphorus and tubular reabsorption of phosphorus became normal, in addition, 1, 25-dihydroxyvitamin D was elevated within normal limit. EMG findings revealed normal motor nerve unit with normal recruitment pattern. Mild myopathy is relatively a common manifestation in patients with osteomalacia. On the other hand, osteomalacia is sometimes caused by tumors, many of which are benign mesenchymal tumors of bone or soft tissue origin.(ABSTRACT TRUNCATED AT 250 WORDS)